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The structure of deformed neutron-rich nuclei in the rare-earth region is of significant interest for both the astrophysics and nuclear structure fields. At present, a complete explanation for the observed peak in the elemental abundances at A~160 eludes astrophysicists, and models depend on accurate quantities, such as masses, lifetimes, and branching ratios of deformed neutron-rich nuclei in this region. Unusual nuclear structure effects are also observed, such as the unexpectedly low energies of the first 2+ levels in some even-even nuclei at N=98. In order to address these issues, mass and β-decay spectroscopy measurements of the 160Eu97 and 162Eu99 nuclei were performed at the Californium Rare Isotope Breeder Upgrade radioactive beam facility at Argonne National Laboratory. Evidence for a gap in the single-particle neutron energies at N=98 and for large deformation (β2~0.3) is discussed in relation to the unusual phenomena observed at this neutron number. [ABSTRACT FROM AUTHOR]

A precision measurement of the β^{+} decay of ^{8}B was performed using the Beta-decay Paul Trap to determine the β-ν angular correlation coefficient a_{βν}. The experimental results were combined with new ab initio symmetry-adapted no-core shell-model calculations to yield the second-most precise measurement from Gamow-Teller decays, a_{βν}=-0.3345±0.0019_{stat}±0.0021_{syst}. This value agrees with the standard model value of -1/3 and improves uncertainties in ^{8}B by nearly a factor of 2. By combining results from ^{8}B and ^{8}Li, a tight limit on tensor current coupling to right-handed neutrinos was obtained. A recent global evaluation of all other precision β decay studies suggested a nonzero value for right-handed neutrino coupling in contradiction with the standard model at just above 3σ. The present results are of comparable sensitivity and do not support this finding.

We present the first measurement of the α-β-ν angular correlation in the Gamow-Teller β^{+} decay of ^{8}B. This was accomplished using the Beta-decay Paul Trap, expanding on our previous work on the β^{-} decay of ^{8}Li. The ^{8}B result is consistent with the V-A electroweak interaction of the standard model and, on its own, provides a limit on the exotic right-handed tensor current relative to the axial-vector current of |C&#95;{T}/C&#95;{A}|^{2}<0.013 at the 95.5% confidence level. This represents the first high-precision angular correlation measurements in mirror decays and was made possible through the use of an ion trap. By combining this ^{8}B result with our previous ^{8}Li results, we demonstrate a new pathway for increased precision in searches for exotic currents.

We place unprecedented constraints on recoil corrections in the β decay of ^{8}Li, by identifying a strong correlation between them and the ^{8}Li ground state quadrupole moment in large-scale ab initio calculations. The results are essential for improving the sensitivity of high-precision experiments that probe the weak interaction theory and test physics beyond the standard model. In addition, our calculations predict a 2^{+} state of the α+α system that is energetically accessible to β decay but has not been observed in the experimental ^{8}Be energy spectrum, and has an important effect on the recoil corrections and β decay for the A=8 systems. This state and an associated 0^{+} state are notoriously difficult to model due to their cluster structure and collective correlations, but become feasible for calculations in the ab initio symmetry-adapted no-core shell-model framework.

The electroweak interaction in the standard model is described by a pure vector-axial-vector structure, though any Lorentz-invariant component could contribute. In this Letter, we present the most precise measurement of tensor currents in the low-energy regime by examining the β-ν[over ¯] correlation of trapped ^{8}Li ions with the Beta-decay Paul Trap. We find a&#95;{βν}=-0.3325±0.0013&#95;{stat}±0.0019&#95;{syst} at 1σ for the case of coupling to right-handed neutrinos (C&#95;{T}=-C&#95;{T}^{'}), which is consistent with the standard model prediction.

The structure of deformed neutron-rich nuclei in the rare-earth region is of significant interest for both the astrophysics and nuclear structure fields. At present, a complete explanation for the observed peak in the elemental abundances at A∼160 eludes astrophysicists, and models depend on accurate quantities, such as masses, lifetimes, and branching ratios of deformed neutron-rich nuclei in this region. Unusual nuclear structure effects are also observed, such as the unexpectedly low energies of the first 2^{+} levels in some even-even nuclei at N=98. In order to address these issues, mass and β-decay spectroscopy measurements of the ^{160}Eu&#95;{97} and ^{162}Eu&#95;{99} nuclei were performed at the Californium Rare Isotope Breeder Upgrade radioactive beam facility at Argonne National Laboratory. Evidence for a gap in the single-particle neutron energies at N=98 and for large deformation (β&#95;{2}∼0.3) is discussed in relation to the unusual phenomena observed at this neutron number.